A fume hood may be generally described as a four sided ventilated enclosed workspace intended to capture or contain exhaust fumes, vapors, and particulate matter generated inside the enclosure thru a duct system with exhaust fan to atmosphere. The purpose of a fume hood is to draw fumes and other airborne matter generated within a work chamber away from a worker, so that inhalation of contaminants is minimized. The concentration of contaminants to which a worker is exposed should be kept as low as possible and should never exceed permissible exposure limits (PELs).
Typically, fume hoods in laboratory operate twenty-four hours a day and exhaust conditioned make up air from the room thru its window openings or bypass openings to the atmosphere. Lower energy consumption has triggered several known methods and apparatus for fume hoods with emphasis on making a stronger vortex formation inside a fume hood chamber or restricting face openings. Some known fume hoods have tried to address the vortex stability inside a fume hood chamber by modulating baffles or modulating a damper behind a baffle. Since the mechanism is hidden and inside the baffle conduit or baffle chamber, it is difficult to monitor any malfunction or repair any defects without decontaminating the entire fume hood and disassembling its components.
In general, known fume hoods are designed either for Variable Air Volume (VAV) or Constant Air Volume (CAV). Known VAV fume hoods maintain constant face velocity at a face opening by varying exhaust air volume with a modulated damper whereas known CAV fume hoods maintain constant exhaust air volume with fixed position or a pressure independent CAV damper and varying face velocity based on a face opening.
Nearly all known fume hoods provide vertical or combination (vertical and horizontal) sashes with counter balance weight, pulley, and cable mechanism. Over time, the vertical sash movement tends to wear out and makes it inoperable. When the sash counter balance weight is at the back of the fume hood, normally it has to be brought out of its place for repair that involves huge expense and down time to remove all the utilities and duct work.
Counter balance weight for the sashes along with associated parts accounts for 20% to 30% of the total weight depending on the liner material which makes it challenging to transport and install the fume hood in one piece.